For opening containers made of plastic coated cardboard and for pouring the contents out, usually either a seam of the container is opened or a corner torn off. In both cases the container cannot be reclosed which means that the once opened container cannot be transported easily and that the contents of the container must be used up rapidly if it is not stable under the influence of the surrounding air.
Containers which do not show the above described disadvantages are e.g. equipped with closure units which are fitted over an opening in the container wall and which consist of a pouring part fixed to the container wall and a closure part removably closing the opening of the pouring part. Such equipped containers are very comfortable in use, but they are rather expensive regarding manufacturing. The closure unit is usually fitted to the container wall material before folding and welding it to form the container or at least before filling the container and it must satisfy the same hygienic and antiseptic standards as the inside surface of the container wall in order to allow long storage of the filled container.
For omitting the described disadvantages of containers with fitted closure units, combinations of containers of plastic coated cardboard with a potential opening and corresponding plug-in closure units have been designed. The combination is usually brought to the market with the plug-in closure unit attached to one side of the filled container, in the same way as drinking straws are attached to the container. The potential opening is a predetermined location on the containers, and is equipped such that it can be opened easily by the consumer by removing a stuck on pull tab and/or by breaking a predetermined breaking point in the container wall or at least in some of its layers when inserting the closure unit, thus forming an opening of a predetermined shape.
Such a plug-in closure unit has inner and outer retaining means and when it is positioned in the container opening, the edge of the container wall is retained between these retaining means.
Conditions to be satisfied by a combination of a container and a plug-in closure unit are the following:
The potential opening in the container must be openable easily, but it must not be a weak point of the container such that the container with the potential opening can be handled in exactly the same way as a similar container without a potential opening or a container with a fitted closure unit. PA1 The closure unit must be fiat, such that it can be packed with the container without causing difficulties regarding transport and storage of the combination. PA1 The consumer must be able to plug in the closure unit into the potential opening with a reasonable amount of force and without deforming the container wall too much (especially important for containers which are completely filled). PA1 The plugged-in closure unit must be openable without coming off the container. PA1 The container with plugged-in closure unit must be tight regarding tightness between container and closure unit as well as regarding tightness between closure part and pouring part of the closure unit. PA1 If besides all the above named conditions, further conditions regarding easy pouring and clean reflux of the contents into the container after pouring can be satisfied, then the combination of container and closure unit is very advantageous. The same applies for conditions regarding prolonged service time of the container with plugged-in closure unit without deterioration.
In the publication EP-A2-291112 a combination of a container and a plug-in closure unit is described, which combination satisfies the above described conditions more or less. The closure unit of the described combination consists of a pouring part and a closure part connected by a hinge, which closure part features an opening lip positioned opposite the hinge and serves to open the closure unit. The above condition of the potential opening as well as the condition of the flatness of the closure unit are satisfied well, but for the sake of its flatness, the pouring characteristics of the closure unit are very poor and must be assisted by a protruding rim on the container.
The closure unit of the described combination is fitted to the container by positioning it on the opening and then pressing it into it with a force perpendicular to the container surface. There is a snap running all round the outside of the pouring part, serving as inner retaining means. The outermost edge of the snap circumscribes an area which corresponds to the container opening in shape, but is larger than it. The snap is meant to be pushed through the opening and to retain the pushed-in closure unit in the opening. On pushing the snap through the opening, the cardboard edge all round the container opening is stressed and at least temporarily deformed. For this reason the force necessary for inserting the closure unit into the opening is rather large. At the same time the whole container wall is being pressed towards the inside of the container, which might cause the contents to be spilled.
Positioning and insertion of the closure unit into the opening is facilitated by a conical sliding face leading up to the edge of the snap. The ease with which the closure unit can be inserted into the opening is determined by the steepness of this sliding face which determines also how deep the fitted pouring part extends into the inside of the container, and therefore also determines its flatness.
Opening characteristics and tightness of the known combination of container and plug-in closure unit are satisfactory, at least for only short service. If the container with inserted closure-unit is in use over a longer period of time, the liquid contents is sucked up by the cardboard in the region of its edge around the opening, where its coating is interrupted. This causes deterioration of the tightness between container and closure unit and does not look nice.
It is thus the object of the invention to create a combination of container and plug-in closure unit which satisfies all the above mentioned conditions and satisfies them better than the combination of container and closure unit according to the state of the art. It is further an object of the invention to show a method for manufacturing a container for the combination.